atomic number protons + neutrons = atomic mass

ISOTOPES

FROM THE PERIODIC TABLE – WHAT NUMBER EQUALS THE NUMBER OF PROTONS?

Atomic Number

FROM THE PERIODIC TABLE – HOW IS THE MASS OF A “REGULAR” (MOST ABUNDANT) ATOM DETERMINED?

Protons + Neutrons = Atomic Mass

AN ISOTOPE IS DEFINED AS… An Atom of an Element that has the

same number of protons as another atom of the same element but a different number of neutrons.

THE ELEMENT HYDROGEN, FOR EXAMPLE, HAS THREE COMMONLY KNOWN ISOTOPES: PROTIUM, DEUTERIUM AND TRITIUM.

SINCE THE ATOM HAS THE SAME PROTONSIsotopes of an element have the same

chemical properties.

LITHIUM

ONE WAY TO WRITE THE ISOTOPE

ANOTHER WAY TO WRITE THE ISOTOPE

Na - 23

WHY ARE THE MASSES ON THE PERIODIC TABLE DECIMAL NUMBERS?

Average of all the isotopes of that element

IF AN ATOM HAS A DIFFERENT NUMBER OF NEUTRONS May make the element have a different

radioactivity.

Radioactivity is the release of energy and matter that results from changes in the nucleus of an atom

An isotope that is radioactive is called a radioisotope or radionuclide. The

RADIOACTIVE ISOTOPESOften called Radioisotopes

How does this happen?An additional neutron or two may upset

the nucleus and cause the atom to become unstable. In an unstable atom, the nucleus changes by giving off a neutron to get back to a balanced state. As the unstable nucleus changes, it gives off radiation and is said to be radioactive.

ELEMENTS WITH ATOMIC # GREATER THAN 83 Are Radioisotopes Have unstable nuclei and are

radioactive.

ELEMENTS WITH ATOMIC # GREATER THAN 83 AND LESSHave isotopes with a stable nucleus

And

Most have at least one radioisotope with an unstable nucleus.